STABILIZATION OF TERNARY COMPOUNDS VIA ORDERED ARRAYS OF DEFECT PAIRS

First-principles calculations show that the defect pair (2V(Cu)(-) + I n-Cu(+)) in CuInSe2 has an unusually low formation energy, due both to the relative ease of forming Cu vacancies (V-Cu) and to the attractiv e interactions between V(Cu)(-) and In-Cu(2+). The defect pair is pred icted to be electrically inactive. This explains the surprising electr ical tolerance of CuInSe2 to its huge (similar to 1%) concentration of native defects. An attractive interaction among the defect pairs is f urther predicted to lead to a crystallographic ordering of the pairs, explaining the observed, but hitherto surprising, structures CuIn5Se8, CuIn3Se5, Cu2In4Se7, etc.